Are Split Stacks Superfluous on AMD64 Architectures?

Split Stacks: Unnecessary on AMD64?

It has been suggested that using the split stack runtime model is superfluous on 64-bit architectures. This implies that the vast address space on 64-bit systems can handle potentially large numbers of threads without this additional stack management scheme.

Do Experts Agree?

While Ian Lance Taylor hints at this notion by suggesting that a 64-bit address space can accommodate thread stacks, bstrie explicitly states that the overhead and limited use case of split stacks on 32-bit platforms make them unnecessary on 64-bit systems.

Why Unnecessary on AMD64?

Split stacks on 64-bit AMD64 architectures are indeed unnecessary because:

• Vast Virtual Address Space: The 64-bit virtual address space provides a large enough address range to accommodate millions of stack address ranges. Each range can be as extensive as an entire 32-bit address space.
• Dynamic Memory Management: In the flat memory model used on AMD64, the hardware MMU facilitates seamless memory management. The system reserves large chunks of virtual address space for new stacks but maps only a portion (typically 4 kB) to physical memory.
• On-Demand Mapping: As the stack grows or shrinks, the OS dynamically adjusts the MMU mappings to map additional pages of virtual address range to physical memory.
• Performance Optimization: This approach enables stacks to expand and contract efficiently while maintaining contiguous virtual addresses, minimizing code overhead during function prologues.
• Scalability: The mechanism allows for the creation of millions of stacks that can grow as needed, consuming only the memory they utilize.

In contrast to the sophisticated mechanisms employed on AMD64, the current Go implementation lacks these optimizations, making split stacks unnecessary on this platform.

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